Meet the giant water bugs!

This time I’m actually going to write about giant water bugs, as promised! As I write this, I am sitting in a lab at Arizona State University measuring the oxygen consumption of water bug eggs. I’ll write more about that in another post, but first allow me to introduce you to the giant water bugs!

This gorgeous creature is Lethocerus medius:

Lethocerus medius

Isn’t he a formidible looking insect? It’s hard to tell from the picture, but this male is about 2.5 inches long from the top of the head to the tip of the abdomen, and that doesn’t include the long, pointy bits sticking out of the back! The size of these bugs is where they get the “giant” part of their common name. They get “water” because they are aquatic insects and live in water. The “bug” portion of the common name comes from the fact that they are true bugs, i.e. they belong to the insect order Hemiptera . The common name giant water bug thus tells you a lot about these insects – the giant water bugs are really big aquatic insects!

The giant water bugs belong to the family Belostomatidae. What makes an insect a belostomatid? First, let’s review why this insect is a true bug. We can tell he is a bug because there are hemielytra present and, if you flip him on his back and look under his head, his mouthparts are piercing-sucking mouthparts. These are the characteristics of true bugs. You can read more about what makes an insect a bug in my post about the true bugs.

You can tell this is a belostomatid, as opposed to any other true bug, because it has the following:

1. Raptorial forelegs. Predatory insects, such as the giant water bugs, mantids, and assassin bugs, frequently have enlarged forelegs to help them grab and hold their food. If you eat live animals, it’s important that you are able to subdue them! Raptorial forelegs help you do that – they’re full of huge, strong muscles. For a comparison in humans, think of a skinny, nonathletic 10 year old and a professional weight lifter (or Fezzik in The Princess Bride!). Who is going to be able to lift more and/or hold onto something more tightly? The weight lifter, of course, because he has bigger, stronger, and better developed muscles than the 10 year old. The same thing goes with insects. Big forelegs help you grab and subdue prey so you can eat your food. (Interesting aside: there is another type of enlarged foreleg, called a fossorial foreleg, that helps insects that live underground! They need strong muscles in their forelegs to help themdig and move through dirt. If you’ve ever seen a mole cricket, you know what these look like.)

2. Swimming hairs on the legs. See all that brushy stuff coming off the legs? Those are called swimming hairs. Insects have a hard time moving through water and have all kinds of adaptations that help improve their mobility. Having thick hairs on your legs helps you swim better than if your legs are smooth. Think about the way we relatively hairless humans swim. Which is easier: swimming with flippers or swimming without them? It’s easier to swim with flippers because the increase your surface area. By attaching flippers, you are effectively making your feet bigger and flatter. More of your “body” is coming into contact with the water with each kick, so you move further and with less effort than you would without the flippers. Swimming hairs work the same way. They are nature’s swimming flippers!

3. Retractable respiratory appendages. Take a second look at those long pointy bits sticking off the back of the Lethocerus in the picture above. Those are respiratory appendages, called respiratory siphons or air straps depending on which type of water bug you’re looking at. What makes the water bugs different from other insects with respiratory appendages (such as the water scorpions – I’ll be posting about these sometime as well as they include my very favorite insect!) is they are able to retract theirs, pulling them mostly or entirely within their bodies! So why do giant water bugs have these structures? Well, giant water bugs require air to survive, the same air that you and I breathe. I’ll write more about giant water bug respiration in a future post (this is something I study in my lab), but for now just know that these structures help the giant water bugs collect air. Not all giant water bugs have the long siphons though. The giant water bug in the image below is Abedus herberti. Take a look at the respiratory appendage indicated by the arrow:

Abedus herberti. Arrow points to the air straps.

Most of the giant water bugs actually have these little short air straps rather than the long respiratory siphons of Lethocerus, but both types of appendages work the same way. Regardless of the type of appendage, all water bugs are able to pull them into their bodies.

So now we know that belostomatids are true bugs and that they have raptorial forelegs, swimming hairs on their legs, and retractable respiratory appendages. All giant water bugs share these characteristics, regardless of their subfamily, genus, or species. Next time I’ll delve a little bit deeper into the different types of water bugs found in the U.S. and then talk a bit about what I’m doing with my resrearch during my visit to ASU. Stay tuned!

My husband pulled a live giant water bug out of our pool. We haven’t cleaned or hooked it up yet for the summer season. We’ve had small swim my bugs in there before but never a big one like this. We are from Minnesota, so is this common here? I took a picture of it if you’d like me to send it? Thank you.

You definitely have water bugs in your state. If it was one of the really big ones, it was Lethocerus americanus and if it was less than an inch long you had Belostoma flumineum. I’d love to see a photo if you’re willing to share! You can send it to dragonflywoman at outlook dot com.